Switch assembly, electric machine having the switch assembly, and method of controlling the same

ABSTRACT

A pump assembly for pumping a liquid and a method of controlling the pump assembly. The pump assembly includes a motor coupled to a pump, and an electronic switch assembly electrically connected to the motor to control the current through the motor. The electronic switch assembly includes an electronic switch, a generator that provides a substantially periodic pulsing signal, a circuit control configured to provide a second signal, and decision logic connected to the generator, the circuit control, and the electronic switch. The decision logic receives the periodic pulsing and second signals and generates a control signal that selectively controls the electronic switch based on the periodic pulsing and second signals.

RELATED APPLICATIONS

This application is a divisional application of co-pending U.S. patentapplication Ser. No. 11/081,394, filed on Mar. 16, 2005, issued as U.S.Pat. No. 7,183,741.

FIELD OF THE INVENTION

The present invention relates to an electronic switch assembly and, moreparticularly, an electronic switch assembly that controls currentthrough a circuit.

BACKGROUND

Single-phase induction motors of the split phase and capacitor starttypes typically have the start winding connected to the power sourcewhen starting the motor. Once started, however, it is common to removethe start winding, resulting in the motor being more efficient. Onereason for the removal of the start winding and start capacitor (ifpresent) is that the start winding and the start capacitor are nottypically designed for continuous duty. That is, these components willfail if left permanently in the circuit. A common solution to thisproblem is connecting a start switch in series with the start winding(and start capacitor) for controlling current through the start winding.

The most common implementation of a start switch for the above motors isa centrifugal switch mounted on the shaft of the motor. The centrifugalswitch senses the shaft speed of the motor and opens the start windingcontacts at the appropriate speed. This speed is typically around 75% to80% of the rated running speed of the motor.

There are some problems associated with a motor including a centrifugalswitch. Because the switch is opening an inductive load, a large sparkoccurs when the contacts open. This sparking pits the switch contactsand ultimately results in the switch failing. Another problem with themechanical switch is that it must be adjusted in production to get anaccurate switch-out speed. This is another step in the productionprocess, which adds cost. Also, if adjustment difficulties arise, thisstep can slow production of the motor. Another frequently cited problemis that the switch must be mounted on the shaft of the motor and, thus,limits packaging options. The switch, assembly adds length to the motor,which makes motor placement in tight quarters more challenging. A lesserproblem is that the switch makes noise when it opens and closes. Someusers may find the noise objectionable.

SUMMARY

One alternative to a motor including a centrifugal start is a motorhaving an electronic start switch. In one embodiment, the inventionprovides a new and useful electronic switch assembly used to control thecurrent through a circuit. As used herein, a circuit is a conductor orsystem of conductors through which an electric current can or isintended to flow. An example circuit is the start winding and startcapacitor (referred to herein as an auxiliary circuit) of a single-phaseinduction motor of the capacitor start type. However, the electronicassembly is not limited to induction motors of the capacitor start type.

In one construction of the electronic switch assembly, the assemblyincludes a power supply block, a switch control block, and a circuitcontrol block. As used herein, a block is an assembly of circuits and/orcomponents that function as a unit. The power supply block powers theelectronic switch assembly. The switch control block includes anelectronic switch and, generally speaking, opens (or closes) the switchbased on a signal received from the circuit control block.

In another embodiment, the invention provides an electric machine (e.g.,a motor) having a winding (e.g., a start winding) controlled by theelectronic switch assembly. In yet another embodiment, the inventionprovides an electric machine having a capacitor (e.g., a startcapacitor) controlled by the electronic switch assembly. For example,the electronic switch assembly can be used for controlling a start boostcapacitor of a hermetically sealed compressor. It is envisioned that theelectronic switch assembly can control other auxiliary circuits.

It is also contemplated that aspects of the electronic switch assemblycan be used in other applications. For example, the electronic switchassembly can be used to control the motor of a sump pump. Other aspectsof the invention will become apparent by consideration of the detaileddescription and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electrical schematic of a motor including an electronicswitch assembly.

FIG. 2 is a block diagram of a representative electronic switch assemblycapable of being used in the circuit shown in FIG. 1.

FIG. 3 is an electrical schematic of an exemplary power source capableof being used in the electronic switch assembly of FIG. 2.

FIG. 4 is an electrical schematic of an exemplary switch control blockand circuit control block capable of being used in the electronic switchassembly of FIG. 2.

FIG. 5 is an electrical schematic of a portion of the electricalschematic shown in FIG. 4 and, specifically, is an electrical schematicof a voltage sense circuit, a generator circuit, a NAND gate, and aswitch driver.

FIG. 6 is an electrical schematic of a portion of the electricalschematic shown in FIG. 4 and, specifically, is an electrical schematicof a start-up set circuit, a timer circuit, a current sense circuit, anda latch circuit.

FIG. 7 is a graph comparing a current in Amps through the auxiliarycircuit of a single-phase, capacitor-start induction motor against timein milliseconds, and a percent speed of the motor against time inmilliseconds.

FIG. 8 is an electrical schematic of a motor coupled to a hermeticcompressor, the motor including an electronic switch.

FIG. 9 is an electrical schematic of a sump pump including an electronicswitch assembly.

FIG. 10 is a block diagram of a representative electronic switchassembly capable of being used in the circuit shown in FIG. 9.

FIG. 11 is an electrical schematic of an exemplary power source capableof being used in the electronic switch assembly of FIG. 9.

FIG. 12 is an electrical schematic of an exemplary switch control blockand circuit control block capable of being used in the electronic switchassembly of FIG. 9.

FIG. 13 is an electrical schematic of a portion of the electricalschematic shown in FIG. 12 and, specifically, is an electrical schematicof a voltage sense circuit, a generator circuit, a NAND gate, and aswitch driver.

FIG. 14 is an electrical schematic of a portion of the electricalschematic shown in FIG. 12 and, specifically, is an electrical schematicof a liquid level sense circuit, start-up reset circuit, an alarm drivercircuit, and a latch circuit.

FIG. 15 is a side view of one construction of the electronic switchassembly shown in FIG. 10.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. The terms “connected,” “coupled,” and“mounted” and variations thereof herein are used broadly and, unlessotherwise stated, encompass both direct and indirect connections,couplings, and mountings. In addition, the terms connected and coupledand variations thereof herein are not restricted to physical andmechanical connections or couplings.

FIG. 1 schematically represents a single-phase, capacitor startinduction motor 100. The motor 100 includes a main winding 105, a startwinding 110, a start capacitor 115, and an electronic switch assembly120. Unless specified otherwise, the description below will refer to themotor 100. However, the invention is not limited to the motor 100. Forexample, the electronic switch assembly 120 described below can be usedwith a single-phase, split-phase induction motor; a capacitor-start,capacitor-run induction motor (an example of which will be discussed inconnection with FIG. 8), and similar induction motors. It is alsoenvisioned that the electronic switch assembly 120 (or aspects of theswitch assembly 120) can be used with other motor types and otherelectric machines, where the electronic switch assembly 120 controlscurrent through a circuit of the motor or machine. It is even envisionedthat the electronic switch assembly 120 (or aspects of the switchassembly) can be used with any circuit, where the switch assembly 120controls current through the circuit. For example, FIGS. 9-15 disclose asump-pump controller that incorporates aspects of the electronic switchassembly.

With reference to FIG. 1, the main winding 105, the start winding 110,and the start capacitor 115 are conventional components of acapacitor-start induction motor. It is envisioned that other componentscan be added to the motor 100 (see, for example, FIG. 8), and FIG. 1 ismeant only to be a representative induction motor capable of being usedwith the electronic switch assembly 120.

FIG. 2 shows a block diagram of one construction of the electronicswitch assembly 120. With reference to FIG. 2, the electronic switchassembly includes a power supply 200, a switch control block 205, and acircuit control block 210. FIGS. 3 and 4 are detailed electricschematics showing one exemplary electronic switch assembly 120.

The power supply 200 receives power (e.g., 115 VAC or 230 VAC power)from a power source and provides a regulated (i.e., a constant orconsistent) voltage. For the construction shown in FIG. 2, the powersupply 200 is connected to the power line and provides a direct current(e.g., a −5 VDC) power.

FIG. 3 is a detailed schematic showing one exemplary power supply 200capable of being used with the electronic switch 120. With reference toFIG. 3, the power supply 200 includes resistors R1, R12, and R23;capacitor C5; diode D6; Zener diodes D5 and D9; and transistor Q7.During operation, when a positive half-cycle voltage is across the powersupply 200, diode D6 blocks current through the power supply. When anegative half-cycle voltage is across the power supply 200, diode D6conducts causing current to flow through resistor R1, thereby chargingcapacitor C5. Zener diode D5 begins conducting when capacitor C5achieves a voltage determined by the Zener diode D5, thereby limitingthe voltage across capacitor C5. Resistor R12 dissipates the charge ofcapacitor C5 when power is removed from the power supply 200, allowingthe electronic switch assembly 120 to reset.

One feature of the circuit shown in FIG. 3 is that the circuit preventsthe electronic switch 120 from working should the motor 100 be hooked tothe wrong supply voltage. To provide some background, motor manufacturesfrequently design motors for dual voltage operation (e.g., 115 or 230VAC operation) to keep the number of different motor models produced toa minimum. A common mistake by technicians is to hook a 115 VACconfigured motor to a 230 VAC power line. When power is applied to themotor, the electronic switch will perform as normal and the motor willstart (if there were no voltage clamp circuit). When the switch circuitturns off the start winding, however, the triac will need to block alarge voltage (e.g., 1200 V). The power supply clamp keeps the motorfrom starting and, thus, the triac is required to block a muchrelatively smaller voltage (e.g., 350 V). Because the motor did notstart, the clamp circuit has the additional benefit of alerting theinstaller that something is wrong.

Referring once again to FIG. 3, transistor Q7, resistor R23, and Zenerdiode D9 form the power supply clamp circuit. More specifically, Zenerdiode D9 has a set reverse breakdown voltage (e.g. 200 VDC) that resultsin the Zener diode conducting when the voltage applied to the powersupply 200 is greater than the designed motor voltage (e.g., 130 VAC).When Zener diode D9 conducts, transistor Q7 switches on, therebyshorting the power supply. This circuit prevents the electronic switchassembly 120 from working should the motor be hooked to the wrong supplyvoltage by keeping the power supply 200 from powering the circuit.

Referring again to FIG. 2, the electronic switch assembly 120 includes aswitch control block 205. The switch control block 205 includes a switch215 connected in series with the circuit to be controlled. For theconstruction shown, the switch 215 is connected in series with the startwinding 110 and the start capacitor 115. The switch 215 can be anyelectronic switch that prevents/allows current through the switch 215 inresponse to a control signal. An example switch 215 is a triac. In onespecific construction the electronic switch 215 is an “AC Switch” brandswitch, Model No. ACST8-8C, produced by ST Mircoelectronics of France,which also provides a high voltage clamping device to the triac in thesame package to give the triac better line transient immunity andability to switch inductive loads. Unless specified otherwise, theswitch 215 for the description below is a triac.

Referring again to the construction shown in FIG. 2, the switch controlblock 205 includes a generator 220, and NAND gate 225. The generator 220provides a signal to the NAND gate 225, which compares the generatedsignal with a signal from the circuit control block 210 (describedbelow). The result of the NAND gate 225 controls the switch 215. Beforeproceeding further, it should be noted that, while the electronic switchshown is described with the NAND gate 225, the circuit can be readilyredesigned for other gate types.

When the switch 215 is a triac, the generator 220 can be a pulsegenerator and the switch control 205 can also include a voltage sensecircuit 230. Generally speaking, a triac is a bidirection gatecontrolled thyristor capable of conducting in either direction inresponse to a gate pulse. Therefore, the triac does not require a fixedcontrol (or gate) voltage to allow current through the triac. Instead,the generator 220 can be a pulse generator that provides control pulses.To assist the pulse generator, the switch control block 205 includes thevoltage sense circuit 230. The voltage sense circuit 230, generally,monitors the voltage applied to the switch 215 (i.e., the appliedvoltage to the auxiliary circuit) and generates pulses based on theapplied voltage. For example, the voltage sense circuit 230 can monitorthe voltage applied to the triac and generate pulses (also referred toas gating pulses) in relation to the zero crossings of the appliedvoltage. The pulses are applied to the NAND gate 225. The NAND gate 225decides whether a gating pulse should or should not be applied to thetriac switch 215 based on the conditions of the circuit control block210, the result of which controls current through the triac 215. It isenvisioned that the voltage sense circuit 230 and the generator 220 canbe designed differently for other types of gate logic and other types ofswitches (e.g., other types of electronic devices).

FIG. 5 is a detailed schematic showing one exemplary switch controlblock including a triac Q1, a triac voltage sense circuit 530, a pulsegenerator 520, a NAND gate U1D, and a switch driver 570. The triacvoltage sense circuit 530 includes resistors R10, R11, R18, R19, R20,R21, and R22; diode D3; Zener diode D4; transistor Q5; and NAND gateU1C. The pulse generator 520 includes capacitor C1 and resistor R3. Theoutput driver 570 includes resistor R5, R7, R8, R16, and R17; andtransistors Q3 and Q4.

One method to keep the cost of an electronic circuit as low as possibleis to keep the current supplied by the power supply as low as possible.One way to help accomplish this in an electronic switch circuit is touse a triac as the switch 215. A triac has the benefit of being abidirectional gate controlled thyristor that only requires repetitivepulses to continuously conduct. Therefore, rather than providing acontinuous signal to the triac (i.e., via the NAND gate 225), thevoltage sense circuit 530 and generator circuitry 520 only need togenerate short continuous pulses (e., 25 μs) where each pulse isgenerated each half cycle of tie voltage applied to the triac switch Q1.

With reference to FIG. 5, the voltage sense circuit 530 monitors thevoltage across the triac (referred to as the triac voltage) anddetermines whether the absolute value of the triac voltage is greater athreshold (e.g., 5V). When the absolute value of the triac voltage isgreater than the threshold, a logic 0 is applied to pin 9 of the NANDgate U1C, thereby resulting in a logic 1 being applied to pulsegenerator 520. The voltage at pin 8 begins charging capacitor C1 andpulls pin 12 high at NAND gate U1D. A logic 1 is applied to pin 12 ofU1D for the time constant of capacitor C1 and resistor R3. Therefore,the result of the voltage sense circuit 530 and generator 520 circuitryis that pulses are provided to NAND gate U1D, the pulses are onlygenerated when the triac voltage passes through zero voltage to thepositive or negative threshold (i.e., are generated just after each zerocrossing event), and the pulses are narrow relative to the AC cycle ofthe power source. The switch driver 570 drives the triac Q1 based on theoutput of NAND gate U1D. While not necessary, the switch driver 570 isused because the triac Q1 can float off of ground. The driver 570prevents voltage from feeding back into NAND gates U1C and U1D if thetriac Q1 does float.

A subtle feature of the circuit shown in FIG. 5 relates to the linelabeled 575 in FIG. 5. Line 575 locks out the voltage sense circuit 530when the pulse is being applied to the gate of the triac Q1. Thisfeature makes sure the full current pulse is applied to the triac Q1and, thus, prevents teasing the triac Q1 ON. More specifically, as thecurrent pulse is applied to the gate, the triac Q1 will startconducting. The voltage across the main terminals of the triac Q1 willgo to near zero without line 575. This can fool the voltage sensingcircuit 530 into thinking the triac Q1 is fully conducting, and thecircuit terminates the current pulse to the gate. Line 575 prevents thisby forcing the NAND gate U1C to provide a logic 1 result during the timeconstant of resistor R3 and C1.

Before proceeding further it should be noted that, in someconstructions, the voltage sense circuit 230, generator 220, and NANDgate 225 are not required. That is, the circuit control block 210(discussed below) can directly control the switch 215.

Referring again to FIG. 2, the electronic switch assembly 120 includes acircuit control block 210). For the construction shown in FIG. 2, thecontrol block 210 includes a latch 235, a startup set 240, a currentsense circuit 245, an OR gate 250, and a limit timer 255. the latch 235,which is shown as an SR latch, provides outputs to the switch controlblock 205 based on values received at the latch inputs, which are shownas inputs S and R. The outputs determine whether the switch 215 is on oroff. Other latches and other arrangements for the SR latch can be used(e.g., if NAND gate 225 is replaced by an AND gate).

The startup set 240 sets the latch in the set condition while the motorpower supply 200, and consequently the electronic switch assembly,powers up. This ensures that the start winding 110 is energized for atleast the duration of the set pulse, and that the current sense circuit245 (discussed below) stabilizes before it is allowed to open switch215. An exemplary start-up circuit 640 is shown in FIG. 6. The startupset circuit 640 includes resistors R4 and R6, capacitor C2, diode D2,Zener diode D1, and transistor Q2. The duration of the start-up periodis set by how long it takes for capacitor C2 to charge to a voltagegreater than the reverse breakdown voltage of Zener diode D1, and thusturn on transistor Q2.

There are two ways that the latch 235 can be reset: A) either themagnitude of the current through switch 215 (i.e., through thecontrolled circuit) is greater than a threshold or a timer times out.For example, if the rotor of the motor was locked on startup, themagnitude of the start winding current would never increase and thestart winding would remain connected until the thermal switch protectingthe motor finally opens. With this high current flowing continuously inthe motor start winding, the triac switch and current sensing resistor(discussed below) would get very hot and would likely fail. To keepcircuit costs low, the limit timer is added to terminate the startwinding current after a time period (e.g., 1 to 1.5 seconds), whetherthe motor is started or not. An exemplary timer circuit 655 is shown inFIG. 6 as resistor R9 and capacitor C4, where the period for the timercircuit 655 is determined by the RC time constant of resistor R9 andcapacitor C4. The timer changes the value of the signal (e.g., from alogic 0 to a logic 1) provided to the OR gate 250 (FIG. 2) after thetime period.

Also provided to OR gate 250 is the result of the current sense circuit245. Referring again to FIG. 2, the current sense circuit 245 senses thecurrent through the switch 215 and compares the sensed value to athreshold. The result of the OR gate is provided to the latch 235,thereby controlling the latch 235, the NAND gate 225, and ultimately theswitch 215. More specifically, if either the current sense circuit 245or the limit timer 255 generates a logic 1, the SR latch resets, therebycontrolling the NAND gate 225 and the switch 215. Before proceedingfurther, it should be noted that either the timer 255 or the currentsense circuit 245 can be removed from the circuit control block 210.Additionally, in other constructions, other sensors or circuits can beused in place of the current sense circuit 245 (e.g., a voltage sensor)and the current sense circuit 245 can sense other circuits (e.g., themain winding circuit) or components.

FIG. 6 is a detailed schematic showing one exemplary circuit controlblock including set/reset latch circuit 635, startup set circuit 640,timer circuit 655, and current sense circuit 645. The set/reset latchcircuit 635 includes NAND gates U1A and U1B. The current sense circuit645 includes resistors R2, R13, R14, and R15; capacitor C6; diode D7;and transistor Q6. For the current sense circuit, current flows fromtriac Q1 (FIG. 5) through resistor R2 (FIG. 6). This creates a voltagedrop across resistor R2, which is used for sensing. Current from thenegative half cycle of the applied power flows through diode D7 andresistor R13 to charge capacitor C6. The charging of capacitor C6relates to the voltage drop across resistor R2. When the voltage dropacross resistor R2 is greater than a varying threshold, switch Q6activates and pulls pin 5 of U1B low. This results in the reset of latch635 and, then, latch 635 provides a logic 0 to NAND gate U1D, therebydeactivating triac Q1.

One feature of the current sense circuit 645 is that the circuit 645scales the switch-out point based on the initial start winding current.To provide some background, during low line conditions, the startwinding current is lower and, during high line conditions, the startwinding current is higher. This can potentially create a switch-outspeed error. To compensate for this, the first two or three cycles ofstart winding current charges capacitor C6 up to a value 0.7 volts(i.e., the diode forward drop) less than the peak voltage across thecurrent sensing resistor R2. This sets the trip threshold value for thecircuit. When the start winding current magnitude rapidly grows as themotor reaches operating speed, the voltage from base to emitter ontransistor Q6 becomes sufficient to turn transistor Q6 ON. Therefore,the current sense circuit 245 scales the switch-out point to detect whenthe current of the auxiliary circuit flares.

One feature of the electronic switch assembly shown in FIG. 4 is thatthe assembly uses only three connections for connecting to the motor.Moreover, each connection is readily available. This reduces thecomplexity of adding the switch assembly shown if FIG. 4, andpotentially reduces assembly time. However, for other constructions,more connections may be required.

As stated earlier and best shown in FIG. 1, the electronic switchassembly 120 can control current through the start winding 110 and thestart capacitor 115 of a single-phase, capacitor-start induction motor.In operation, as power is applied to the motor 100, the power supply 200charges and, when charged, the electronic switch assembly 120 energizes.As the voltage applied to the start winding 110 (and the electronicswitch assembly 120) passes through zero, the voltage sense circuit 230and generator 220 senses voltage on the switch 215 and generates pulsesin relation to the zero crossings of the voltage. The pulses areprovided to NAND gate 225.

The NAND gate 225 receives a control signal from latch 235. Based on thecontrol signal, the NAND gate 225 triggers (or “re-triggers”) the switch215 into conduction. For the construction shown, when the NAND gate 225receives a logic 1 from the latch 235, the switch 215 conducts, and,when the NAND gate 225 receives a logic 0 from the latch 235, the switch215 prevents current through the auxiliary circuit.

The startup set 240 forces the switch 215, via the latch 235 and NANDgate 225, to conduct for a time interval after the power supplyenergizes the electronic switch assembly. The current sense circuit 245monitors the magnitude of the current flowing through the switchassembly. When the magnitude is greater than a threshold, the currentsense circuit 245 forces, via OR gate 250, latch 235, and NAND gate 225,the switch 215 to prevent current flow through the auxiliary circuit(i.e., to “open” switch 215). Should the motor not come up to speedwithin a time interval, the timer 255 forces, via OR gate 250, latch235, and NAND gate 225, the switch 215 to prevent current flow throughthe auxiliary circuit. Preventing current flow through the auxiliarycircuit prevents current flow through the start winding 110 and thestart capacitor 115.

The electronic switch assembly 120 senses the magnitude of the auxiliarycircuit current to determine the appropriate switch-out point for theauxiliary circuit. FIG. 7 shows a representative auxiliary circuitcurrent waveform 700. It can be seen that as the rotor speeds up(waveform 705), the magnitude of the auxiliary circuit current staysrelatively constant until the motor nears running speed. As the motorapproaches running speed, the magnitude of the current grows rapidlybecause the start winding is no longer contributing to the outputtorque, but is rather fighting with the main winding. The electronicswitch circuit 120) uses the flaring of the current to its benefit todeactivate the auxiliary circuit and, consequently, the start winding.

Referring now to FIG. 8, a motor 100A for controlling ahermetically-sealed compressor 800 is schematically shown with theelectronic switch assembly 120A. The hermetically-sealed compressor 800can be a conventional positive displacement type compressor (e.g., arotary compressor, a piston compressor, a scroll compressor, a screwcompressor, etc.) known in the art and is not discussed further herein.FIG. 8 schematically represents a single-phase, capacitor start,capacitor run induction motor 100A. The motor 100A mechanically controlsthe compressor 800 as is known in the art. The motor 100A includes amain winding 105A, an auxiliary winding 110A (sometimes referred to asthe permanent split winding or even the start winding), and a rotor 805(which can combine with a piston 810 to form a driven member 815), allof which are supported within a hermetically-sealed housing of thecompressor 800. The motor 100A also includes a permanent split capacitor113A, a start capacitor 115A (sometimes referred to as a boostcapacitor), and the electronic switch assembly 120, all of which aresupported outside of the hermetically-sealed housing. The electronicswitch assembly 120 used with the motor 100A can be the same as theelectronic switch assembly described in connection with FIGS. 2-6.

It is common to use a single-phase, permanent split capacitor (PSC)induction motor for operating a hermetically-sealed compressor. Onedeficiency of using the PSC motor is that the motor has difficultiesstarting the compressor if high head pressure is present. A switchcircuit is sometimes included in the motor controller to switch-in theextra start capacitor 115A to boost the start torque of the motor,commonly referred to as a “hard-start kit.” Typically, the startcapacitor 115A is connected in parallel with the permanent capacitor113A. Once started, the switch circuit switches the start capacitor 115Aout for normal operation. For the compressor 800 shown in FIG. 8, theelectronic switch assembly 120 is used to switch the extra startcapacitor 115A in-and-out of the motor controller.

Also as discussed earlier, an electronic switch assembly 120 (or aspectsof the electronic switch assembly 120) can be used with other motortypes and other electric machines where the electronic switch assemblycontrols current through a circuit of the motor or machine. Withreference to FIG. 9, a sump-pump assembly 900 has an electronic switchassembly 920 in a series circuit relationship with a pump motor 925,which can be an induction motor having one or more windings 105. Thepump motor 925 is coupled to a pump 930 and is used for driving the pump930.

FIG. 10 shows a block diagram of one construction of the electronicswitch assembly 920. With reference to FIG. 10, the electronic switchassembly 920 includes a power supply 1000, a switch control block 1005,a circuit control block 1010, and an alarm control block 1012 forcontrolling an alarm 1014. FIGS. 11 and 12 are detailed electricschematics showing one exemplary electronic switch assembly 920.

The power supply 1000 receives power (e.g., 115 VAC or 230 VAC power)from a power source and provides a regulated (i.e., a constant orconsistent) voltage. For the construction shown in FIG. 10, the powersupply 1000 is connected to the power line and provides a direct current(e.g., a −5 VDC) power. FIG. 11 provides a detailed schematic showingone exemplary power supply 1000 capable of being used with theelectronic switch 920. With reference to FIG. 11, the power supply 1000includes resistor R9 a, capacitors C6 a and C8 a, diode D1 a, Zenerdiode D4 a, surge arrestor MOV1 a, and voltage regulator U4 a. Beforeproceeding further, it should be understood that the power supply 200 oraspects of the power supply 200 (e.g., the voltage clamp of power supply200) can replace the power supply 1000 in the electronic switch 920.

Referring again to FIG. 10, the electronic switch assembly 920 includesa switch control block 1005. The switch control block 1005 includes aswitch 1015 connected in series with the circuit to be controlled. Forthe construction shown, the switch 1015 is connected in series with thepump motor 925. The switch 1015 can be any electronic switch thatprevents/allows current through the switch 1015 in response to a controlsignal. An example switch 1015 is a triac. In one specific constructionthe electronic switch 1015 is an “AC Switch” brand switch, Model No.ACST8-8C, produced by ST Mircoelectronics of France, and discussedearlier. Unless specified otherwise, the switch 1015 for the descriptionbelow is a triac.

Similar to the switch control block 205, the switch control block 1005includes a generator 1020, and NAND gate 1025. The generator 1020provides a signal to the NAND gate 1025, which compares the generatedsignal with a signal from the circuit control block 1010 (describedbelow). The result of the NAND gate 1025 controls the switch 1015.Before proceeding further, it should be noted that, while the electronicswitch shown is described with the NAND gate 1025, the circuit can bereadily redesigned for other gate types.

When the switch 1015 is a triac, the generator 1020 can be a pulsegenerator and the switch control 1005 can also include a voltage sensecircuit 1030. Generally speaking, a triac is a bidirectional gatecontrolled thyristor capable of conducting in either direction inresponse to a pulse. Therefore, the triac does not require a fixedcontrol (or gate) voltage to allow current through the triac. Instead,the generator 1020 can be a pulse generator that provides controlpulses. To assist the pulse generator, the switch control block 1005includes the voltage sense circuit 1030. The voltage sense circuit 1030,generally, monitors the voltage applied to the switch 1015 and generatespulses based on the applied voltage. For example, the voltage sensecircuit 1030 can monitor the voltage applied to the triac and generatepulses (also referred to as gating pulses) in relation to the zerocrossings of the applied voltage. The pulses are applied to the NANDgate 1025. The NAND gate 1025 decides whether a gating pulse should orshould not be applied to the triac switch 1015 based on the conditionsof the circuit control block 1010, the result of which controls currentthrough the triac 1015. It is envisioned that the voltage sense circuit1030 and the generator 1020 can be designed differently for other typesof gate logic and other types of switches (e.g., other types ofelectronic devices).

FIG. 13 is a detailed schematic showing one exemplary switch controlblock 1015 including a triac Q1 a, a triac voltage sense circuit 1330, apulse generator 1320, a NAND gate U5Da, and a switch driver 1370. Thetriac voltage sense circuit 1330 includes resistors R5 a, R8 a, and R10a; diode D2 a; Zener diode D3 a; transistor Q3 a; and NAND gate U5Ca.The pulse generator 1320 includes capacitor C5 a and resistor R11 a. Theoutput driver 1370 includes resistors R2 a and R3 a; and transistor Q2a.

As discussed earlier, one method to keep the cost of an electroniccircuit as low as possible is to keep the current supplied by the powersupply as low as possible. One way to help accomplish this in anelectronic switch circuit is to use a triac as the switch 1015. A triachas the benefit of being a bidirectional gate controlled thyristor thatonly requires repetitive pulses to continuously conduct. Therefore,rather than providing a continuous signal to the triac (i.e., via theNAND gate 1025), the voltage sense circuit 1330 and generator circuitry1320 only need to generate Short continuous pulses (e.g., 25 μs) whereeach pulse is generated each half cycle of the voltage applied to thetriac switch Q1 a.

With reference to FIG. 13, the voltage sense circuit 1330 monitors thevoltage across the triac (referred to as the triac voltage) anddetermines whether the absolute value of the triac voltage is greater athreshold (e.g., 5V). When the absolute value of the triac voltage isgreater than the threshold, a logic 0 is applied to pin 9 of the NANDgate U5Ca, thereby resulting in a logic 1 being applied to pulsegenerator 1320. The voltage at pin 8 begins charging capacitor C5 a andpulls pin 12 high at NAND gate U5Da. A logic 1 is applied to pin 12 ofU5Da for the time constant of capacitor C5 a and resistor R11 a.Therefore, the result of the voltage sense circuit 1330 and generator1320 circuitry is that pulses are provided to NAND gate U5Da, the pulsesare only generated when the triac voltage passes through zero voltage tothe positive or negative threshold (i.e., are generated just after eachzero crossing event), and the pulses are narrow relative to the AC cycleof the power source. The switch driver 1370 drives the triac Q1 a basedon the output of NAND gate U5Da.

Similar to the circuit shown in FIG. 5, FIG. 13 includes line 1375. Line1375 locks out the voltage sense circuit 1330 when the pulse is beingapplied to the gate of the triac Q1 a. This feature makes sure the fullcurrent pulse is applied to the triac Q1 a and, thus, prevents teasingthe triac Q1 a ON. More specifically, as the current pulse is applied tothe gate, the triac Q1 a will start conducting. The voltage across themain terminals of the triac Q1 a will go to near zero without line 1375.This can fool the voltage sensing circuit 1330 into thinking the triacQ1 a is fully conducting, and the circuit terminates the current pulseto the gate. Line 1375 prevents this by forcing the NAND gate U5Ca toprovide a logic 1 result during the time constant of resistor R11 a andcapacitor C5 a.

Before proceeding further it should be noted that, in someconstructions, the voltage sense circuit 1030, generator 1020, and NANDgate 1025 are not required. That is, the circuit control block 1010(discussed below) can directly control the switch 1015.

Referring again to FIG. 10, the electronic switch assembly 920 includesa circuit control block 1010. For the construction shown in FIG. 10, thecontrol block 1010 includes a latch 1035, a startup reset 1040, an ORgate 1050, and a liquid level sense circuit 1060. However, othercircuits can be used in addition to or in place of the circuitsdescribed in connection with FIG. 10. For example, other sense circuitsand/or other control parameters can be used to control the electronicswitch instead of the liquid level sensed by the liquid level sensecircuit 1060 (discussed further below).

The latch 1035, which is shown as an SR latch, provides outputs to theswitch control block 1005 based on values received at the latch inputs,which are shown as inputs S and R. The outputs determine whether theswitch 1015 is on or off. Other latches and other arrangements for theSR latch can be used (e.g., if NAND gate 1025 is replaced by an ANDgate).

The startup reset 1040 sets the latch in the reset condition while thepower supply 1000, and consequently the electronic switch assembly,powers up. This ensures that the pump motor 925 is deenergized for atleast the duration of the reset pulse, and that the liquid level sensecircuit 1060 (discussed below) stabilizes before it is allowed tocontrol switch 1015. An exemplary start-up circuit 1440 is shown in FIG.14 as resistor R12 a and capacitor C7 a.

As will be discussed below, the liquid level sense circuit 1060 usesthree plates to sense the level of water in a vessel (such as a crock)and provides a first output to the latch 1035 and a second output to theOR gate 1050. The result of the OR gate 1050 is also provided to thelatch 1035. Therefore, the control of the switch 1015, NAND gate 1025,and the latch 1035 is based on the liquid level sense circuit 1060.

FIG. 14 is a detailed schematic showing one exemplary circuit controlblock including set/reset latch circuit 1435, startup reset circuit1440, NOR gate U3Ca, and liquid level sense circuit 1460. The set/resetlatch circuit 1435 includes NAND gates U5Aa and U5Ba. The liquid levelsense circuit 1460 includes an upper plate 1065 (FIG. 10), a lower plate1070, a reference plate 1075, liquid level sensor U2 a (FIG. 13), andcapacitors C1 a and C9 a. The liquid level sensor U2 a is acharge-transfer sensor, model no. QProx QT114, sold by Quantum ResearchGroup Ltd. The liquid level sensor U2 a acts as a capacitive sensor overmultiple capacitor plates (i.e., the upper, lower, and referenceplates). The capacitance across the upper, lower, and reference plates1065, 1070, and 1075 vary depending on whether water surrounds one ormore of the plates. As the liquid level sensor U2 a measures capacitanceof various levels, it provides varying outputs on lines OUT1 and OUT2.More specifically, if liquid covers the lower plate 1070, the sensedcapacitance is greater than a first threshold and a first signalindicating the first threshold has been passed is provided on OUT1. Thesignal of OUT1 is provided to the reset of the latch 1435. If liquidcovers the upper plate 1465, the sensed capacitance is greater than asecond threshold and a second signal indicating the second threshold hasbeen passed is provided on OUT2. The value of OUT2 is provided to theset of latch 1435 and the timer 1490.

With reference to FIG. 10, when the liquid covers the upper plate 1065,the liquid level sensor provides a value to the latch 1035, setting thelatch 1035. The setting of the latch 1035 provides an “ON” signal toNAND gate 1025, which results in the NAND gate 1025 pulsing the triac1015 based on the pulses provide by the pulse generator 1020 to the NANDdate 1025. Therefore, the “ON” signal provided by the latch 1035 resultsin the triac 1015 closing, the motor 925 operating, and the pump 930pumping. Once the water goes below the lower plate 1070 capacitancefalls and the latch 1035 resets, thereby providing an “OFF” signal. Theissuance of the OFF signal results in the triac 1015 preventing currentfrom flowing through the switch 1015 to the motor 925, and the motor 925turning off.

The electronic switch assembly 920 includes an alarm control block 1012comprising a timer 1090 and an alarm driver 1095. The timer, whichincludes resistors R6 a and R7 a, capacitors C2 a and C3 a, and counterU1 a of FIG. 14, receives an output from the liquid level sense circuit1060 indicating whether a liquid is higher than the upper plate 1065 ofthe liquid level sensor 1060. If the liquid is higher than the upperplate 1065, then the timer 1090 starts. If the liquid is lower than theupper plate 1065, the timer 1090 resets. If the timer 1090 counts apredetermined time period, the timer 1095 provides an output to thealarm driver 1095, which drives the audible speaker 1014. The driverincludes NOR gates U3Aa, U3Ba, and U3Da of FIG. 14.

Referring now to FIG. 15, the figure shows a side view of oneconstruction of the electronic switch assembly 920. As previouslydiscussed, the electronic switch assembly 920 senses a level of a liquidto be pumped and controls the current to the pump motor 925 based on,among other things, the sensed level of the liquid. For the constructionof FIG. 15, the liquid-level sense circuit 1060 is disposed on twoprinted circuit boards (PCBs) 1500 and 1505, which sense the level of aliquid in a vessel (e.g., a sump crock) along an axis (e.g., along thez-axis of FIG. 15). The two PCBs 1500 and 1505 are secured to a supportmember (e.g., the drain outlet pipe 1506) by an attachment member 1508(e.g., clamps, bolts, and nuts). The first PCB 1500 includes a height1510 along the z-axis, a length along the y-axis, and a width along thex-axis. The first PCB 1500 can have multiple layers (e.g., two layers)where a reference foil (acting as the reference plate 1075) and a lowersensor foil (acting as the lower plate 1070) are disposed between afirst and second layer. The reference plate has a height 1515 and alength 1520, and the lower plate has a height 1525 and a length 1530.The reference and lower plates 1075 and 1070 (and the upper plate 1065discussed further below) couple to the other electrical components ofthe electronic switch assembly 920, which are also mounted on the firstPCB 1500 and are housed by a housing 1535 (e.g., plastic molded around aportion of the PCB 1500). A heat sink 1540 is coupled to the electronicswitch assembly 920 and is exposed to the liquid for cooling theelectronic switch assembly 920, particularly the triac 1015 (FIG. 10).

Referring again to FIG. 15, the first PCB 1500 includes a notch 1545disposed between the heights 1515 and 1525 of the reference and lowerplates 1075 and 1070. The notch has a length 1550 that is preferablygreater than the lengths 1520 and 1530 of the reference and lower plates1075 and 1070. In the specific construction shown, the length of thenotch is from one of the edges of the first PCB 1500 to the housing1535.

The second PCB 1505 includes a height 1555 along the z-axis, a lengthalong the y-axis, and a width along the x-axis. The second PCB 1505 (andconsequently the height 1555) is disposed above the first PCB 1500 (andconsequently the height 1510) along the z-axis. The second PCB 1505 alsocan have multiple layers (e.g., two layers) where an upper sense foil(acting as the upper plate 1065) is disposed between a first and secondlayer. The upper plate has a height 1560 and a width 1565. The upperplate 1065 couples to the other electrical components of the electronicswitch assembly 920 via conductors 1570 and 1575.

The buildup of slime and sludge over time contributes to the sensitivityof the switch points of the liquid level sense circuit 1060. The lowersense module 1580 is constructed such that the reference plate 1075 andthe lower sense plate 1070 are separated by the notch 1545 in the firstPCB 1500. This breaks the “leakage” path between the two sensing plates1075 and 1070. There is still a path around the slot, but the length ofthe path is long enough that the capacitance will not be adverselyaffected. Similarly, the upper plate 1065 of the upper sense module 1585is constructed such that the wire connection 1590 to the lower module1580 and the attachment member 1508 c are above the water line, therebyalso breaking the “leakage” path between the reference and upper senseplates 1075 and 1060. It is believed that the connection point 1590 andthe attachment member 1508 c being above the water line should reduceslime and scale building, around the connection point 1590 and theattachment member 1508 c.

Thus, the invention provides, among other things, a new and usefulelectronic switch assembly and motor having the electronic switchassembly. The invention also provides, among other things, a hermeticcompressor having an auxiliary circuit, where the auxiliary circuitincludes a start boost capacitor and the electronic switch assembly.Even further, the invention provides, among other things, a pumpassembly for pumping a liquid where pump assembly comprises anelectronic switch assembly connected to the motor to control the currentthrough the motor. The embodiments described above and illustrated inthe figures are presented by way of example only and are not intended asa limitation upon the concepts and principles of the invention. Variousfeatures and advantages of the invention are set forth in the followingclaims.

1. A liquid-level sensor to sense a liquid having a level with respectto an axis, the liquid level sensor comprising a circuit board having afirst length and a first height, the first height being along the axis,the circuit board comprising a first capacitive plate having a secondlength and a second height, the second height being along the axis, asecond capacitive plate having a third length and a third height, thethird height being along the axis, the third height being disposed abovethe second height, and a notch disposed in the circuit board between thesecond height and the third height with respect to the axis, the notchreducing leakage between the first capacitive plate and the secondcapacitive plate, and a charge-transfer sensor coupled to the first andsecond capacitive plates to measure the capacitance between the firstcapacitive plate and the second capacitive plate.
 2. A liquid levelsensor as set forth in claim 1 wherein the first, second, and thirdlengths are orthogonal to the first, second, and third heights,respectively, and wherein the notch includes a fourth length greaterthan at least one of the second length and the third length.
 3. A liquidlevel sensor as set forth in claim 2 wherein the fourth length isgreater than both of the second length and the third length.
 4. A liquidlevel sensor as set forth in claim 1 wherein the sensor furthercomprises a second circuit board having a fourth length and a fourthheight, the fourth height being along the axis and being disposed abovethe first height, the second circuit board comprising a third capacitiveplate having a fifth length and a fifth height, the fifth height beingalong the axis, and wherein the charge-transfer sensor couples to thethird capacitive plate to measure the capacitance between the firstcapacitive plate and the third capacitive plate.
 5. A liquid levelsensor as set forth in claim 4 wherein the charge-transfer sensor isconfigured to generate a first signal related to the capacitance betweenthe first capacitive plate and the second capacitive plate, wherein thecharge-transfer sensor is further configured to generate a second signalrelated to the capacitance between the first capacitive plate and thethird capacitive plate, and wherein the charge-transfer sensor isfurther configured to compare the first signal to the second signal. 6.A liquid level sensor as set forth in claim 1 wherein the circuit boardincludes a first layer and a second layer, and wherein at least one ofthe first capacitive plate and the second capacitive plate is disposedbetween the first layer and the second layer.
 7. A liquid-level sensecircuit comprising: a substrate having a first length along a first axisand a second length along a second axis, the first axis being orthogonalto the second axis, the substrate defining an indentation having a thirdlength along the first axis; a first capacitive element supported by thesubstrate, the first capacitive element having a fourth length along thefirst axis and a fifth length along the second axis; a second capacitiveelement above the first capacitive element and supported by thesubstrate, the second capacitive element having a sixth length along thefirst axis and a seventh length along the second axis; a sensorconfigured to compare the capacitance between the first capacitiveelement and the second capacitive element to a first value, wherein thethird length is greater than at least one of the fourth length and thesixth length; and wherein the indentation is disposed between the firstcapacitive element and the second capacitive element along the secondaxis and reduces leakage between the first capacitive element and thesecond capacitive element.
 8. The sense circuit of claim 7, wherein thethird length is greater than both of the fourth length and the sixthlength.
 9. The sense circuit of claim 7, wherein the substrate includesa circuit board.
 10. The sense circuit of claim 7, wherein the firstcapacitive element includes a first conductive plate, and wherein thesecond capacitive element includes a second conductive plate.
 11. Thesense circuit of claim 10, wherein the substrate includes a circuitboard having a first layer and a second layer, and wherein the firstconductive plate includes a first metal foil disposed between the firstlayer and the second layer, and wherein the second conductive plateincludes a second metal foil disposed between the first layer and thesecond layer.
 12. The sense circuit of claim 7, further comprising athird capacitive element supported by the substrate above the secondcapacitive element, the third capacitive element having an eighth lengthalong the first axis and a ninth length along the second axis, andwherein the sensor is configured to compare the capacitance between thefirst capacitive element and the third capacitive element to a secondvalue.
 13. The sense circuit of claim 12, wherein the substrate includesa first substrate supporting the first capacitive element and the secondcapacitive element, and wherein the substrate further includes a secondsubstrate supporting the third capacitive element.
 14. The sense circuitof claim 13, wherein the second substrate is disposed a distance fromthe first substrate along the second axis.
 15. The sense circuit ofclaim 12, wherein the second capacitive element is disposed between thefirst capacitive element and the third capacitive element along thesecond axis.
 16. The sense circuit of claim 12, further comprising analarm configured to generate a signal based on the comparison ofcapacitance between the first capacitive element and the thirdcapacitive element to the second value.
 17. A method for operating amotor with a liquid-level sensor assembly including a first substratehaving a first plate with a first length and a first height, a secondplate with a second length and a second height, the first height and thesecond height being along an axis, and an indentation with a thirdlength, the indentation being disposed between the first plate and thesecond plate along the axis, and the third length being greater than atleast one of the first length and the second length, a second substratehaving a third plate, the second substrate placed at a distance from thefirst substrate along the axis, and a sensor electrically coupled to thefirst plate, the second plate, and the third plate, the methodcomprising: detecting a first capacitance between the first plate andthe second plate; detecting a second capacitance between the first plateand the third plate; comparing the first capacitance to a firstthreshold value; comparing the second capacitance to a second thresholdvalue; generating a signal in response to comparing the firstcapacitance to the first threshold value and comparing the secondcapacitance to the second threshold value; and operating the motor inresponse to generating the at least one signal.
 18. The method of claim17, wherein the generating the signal includes generating a first signalin response to comparing the first capacitance to the first thresholdvalue, and generating a second signal in response to comparing thesecond capacitance to the second threshold value.